The present disclosure relates to a battery management system, a battery comprising a battery management system, a motor vehicle comprising the battery management system and a method for monitoring a battery. In particular, the disclosure relates to a battery management system and an associated method for determining and evaluating at least one measured variable from at least one battery module.
It appears that in future new battery systems will increasingly be used both in stationary applications, such as, for example, wind turbines, in vehicles, such as, for example, in hybrid and electric vehicles, and in the consumer sector, such as, for example, in laptops and mobile telephones, and very stringent requirements in respect of the reliability, safety, performance and life of said battery systems will be imposed on these systems.
In particular batteries using lithium-ion technology are suitable for such applications. They are characterized, inter alia, by a high energy density and a low level of self-discharge. By definition, lithium-ion batteries comprise two or more lithium-ion cells which are connected to one another. Lithium-ion cells can be connected to one another by being connected in parallel or in series to form modules and then to form batteries. Typically, a module comprises six or more cells.
DE 10 2009 046 567 A1 discloses a battery which is constructed from a plurality of battery modules, wherein the battery modules are monitored by means of a central battery management system.
As illustrated in FIG. 1, a conventional battery system 10 can have a battery management system 11 comprising a central control device 15, which communicates with a plurality of cell monitoring units 16 (“cell supervision circuit”; CSC), which are each assigned to a plurality of battery cells 14 or battery modules. In the text which follows, depending on the context, all of the battery cells 14 arranged in the battery modules with or without the associated battery management system 11 can be referred to as battery. The battery cells 14 are grouped into battery modules, wherein the precise division of the battery cells into the battery modules is not shown in FIG. 1. The battery management system 11 can be accommodated with battery cells 14 or battery modules in a common housing (not shown). The battery modules can each have a dedicated housing. Improved scalability can be achieved by means of an arrangement of the battery cells 14 in battery modules. In order to monitor correct functioning of the battery cells 14, the battery cells are monitored by the plurality of CSCs 16. In this case, typically a CSC 16 has in each case two battery modules assigned to it. A CSC 16 contains measurement electronics, which monitor the voltage and further parameters. The information obtained by means of the CSC 16 is transmitted via a communication bus 18, for example a CAN bus, to a central control device 15, which evaluates the data from all of the battery cells 14 and, in the event of discrepancies in respect of defined parameters, intervenes with corrections and, if necessary, opens the contactors 17, 19 and disconnects the battery system 10.
The control device 15 has a low-voltage side or a part 22 on the low-voltage side comprising a microcontroller 23 and a high-voltage side or a part 24 on the high-voltage side comprising a microcontroller 25. The low-voltage side 22 and the high-voltage side 24 are connected to one another via galvanic isolation 29. The low-voltage side 22 is connected to a Hall sensor 27 for measuring the battery current, wherein the high-voltage side 24 is connected to a shunt 26 for measuring the battery current. The control device 15 communicates with the vehicle electronics by means of the bus 28. The electrical terminals 12, 13 are used for supplying energy for example for a motor vehicle and/or for recharging the battery.
A further topology for cell monitoring is illustrated in FIG. 2. In this case, the CSCs 16 transmit their information via a daisy chain 32. A CSC 16 in this case directs its data packet to the next CSC, which adds its information and in turn passes this on to the next CSC 16. A cell voltage measuring unit 21 (CVM) is arranged in each CSC 16. The string of CSCs 16 arranged with daisy chain topology is in turn connected to the control device 15.
The monitoring of the cell voltages and the currents and the temperature in respect of specific limit values being overshot or undershot is an essential safety factor in a battery system. ISO standards, in particular ISO 26262: Functional Safety of E/E Systems in Motor Vehicles, require that a certain level of safety ASIL (“Automotive Safety Integrity Level”) is achieved.
In order to ensure sufficient functional safety for the battery system 10, the data from the CSCs 16 are evaluated and compared with one another both on the high-voltage side 24 and on the low-voltage side 22 of the control device 15 in the two redundant microcontrollers 23, 25. The microcontroller 25 on the high-voltage side in this case uses the total voltage of the pack, i.e. all of the battery modules and the total current which is measured by means of the shunt 26, for example. The microcontroller 23 on the low-voltage side measures the voltage of the individual battery cells 14 and the current which is determined via the Hall sensor 27, for example.
The current and voltage need to be interrogated at the same time in order to be able to compute plausible values. In order to be able to compare the values on the high-voltage side 24 and the low-voltage side 22, these data also need to be determined in parallel. In order to obtain a synchronous database, therefore, interrogations are sent by the control device 15 at the same time via the communication bus 18 to the CSCs 16, Hall sensors 27 and the shunt 26, which then ideally signal back simultaneously. In order to meet a high ASIL, the control device also has numerous safety and control functions which include, inter alia, self-monitoring of the control device 15. In addition, the control device monitors the CSCs 16, wherein the data both for the microcontroller 25 on the high-voltage side and for the microcontroller 23 on the low-voltage side are detected by the same CSCs 16.
The known battery management systems have the disadvantage that the control device needs to be programmed, involving a high level of complexity, in order to be able to calculate the plausibility of the CSC data and thus to ensure the required functional safety and to compensate for deficiencies in the often only relatively simple data detection. For this purpose, often very complex computation models need to be used. The data, as already illustrated, are typically recorded using a CAN bus-based or daisy chain-based topology. With the known topologies for monitoring battery cells, a high level of functional safety and therefore a high ASIL therefore require a considerable level of complexity in terms of software. In addition to the high computation complexity involved, the communication bus, preferably a CAN bus, is loaded with many data to be transmitted, with the result that it reaches its capacity limits.